It has long been recognized that despite the comfort provided by an air conditioner in an automobile, a considerable amount of power is required to operate the compressor, power which could be used most advantageously during acceleration and during periods of engine power demand, such as starting from a stop, passing another vehicle and climbing hills.
The patent literature and the market place are not lacking in air conditioner control means responsive to vehicle engine power demands.
An example of the former is Haroldson U.S. Pat. No. 3,462,964 in which a diaphragm is utilized to sense the intake manifold pressure of an engine and operate a switch which, in turn, connects or disconnects the air conditioner from the engine in dependence upon the intake manifold pressure.
The inevitable fatigue and rupture inherent in diaphragm design as well as the difficulty of maintaining a seal over a period of extended use makes it desirable to achieve the economy of diaphragm construction while overcoming its disadvantages.
By substituting a miniaturized mercury U-tube for the diaphragm the shortcomings of the diaphragm type of sensing means are avoided and in one device both sensing and switching capabilities are afforded. Long life and reliability are thereby assured.
Grossman & Wynn, Jr., U.S. Pat. No. 1,078,785 discloses an automatic rheostat in which a mercury U-tube includes successive contacts in a vertical series. However, in this patent, an external resistance is in shunt relation with the contacts and as the mercury level rises through the contacts the current is shunted through the liquid. The device is aptly characterized as a rheostat and is therefore distinguishable from the present invention.
In addition, the throttling effect of the porous plug and adjustment screw in the present device enables the U-tube to be miniaturized while retaining sensitivity and accuracy. Adjustability to various road and load conditions while the car is in motion as well as the provision of an indicator lamp to alert the driver to make the appropriate adjustment before the comfort level of the passenger compartment deteriorates are still further features which, so far as known to applicant, are unique.
It is an object of the invention to provide an air conditioner controller which reduces the load on the engine when most power is needed to move the vehicle.
It is another object of the invention to provide an air conditioner controller which reduces the load on the starter and the battery by declutching the air conditioner compressor during starting and when the car is accelerating, passing another vehicle or climbing hills.
It is a further object of the invention to provide an air conditioner controller in which the compressor operates normally when the vehicle is being driven at a constant speed on level roads or when the vehicle is decelerating, thus using kinetic energy to cool the passenger compartment, or when the engine is idling.
It is yet another object of the invention to provide a generally improved air conditioner controller for vehicles.
Other objects, together with the foregoing are attained in the device shown in the accompanying drawing and disclosed in the subsequent detailed description.